Tip or no tip? (Question in description)

We've had a 3 night hotel stay at the Luxor in LV. We kept the "do not disturb" sign up the entire stay (mostly bc the idea of someone going in my room with all my stuff out while I'm not there freaks me out), and so obviously we did not get any maid service, cleaning, refills, etc.
When you tip, are you tipping because they made it look nice and spruced up for you? Or are you tipping just to pay them? (Answer that in comments)
But since we've had no cleaning done and now it's the last day, should we leave a tip for the lady today or not?
Thanks!

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